Anesthetics and anesthesia are suspicious to induce dementia or aggravate preexistent cognitive deficits with or without evoking postoperative delirium. In animal trials various anesthetics induce increased levels of misfolded amyloid beta and protein tau, the molecular substance of pathophysiologic brain tissues of demented patients. The amount of those markers seems to correlate well with the degree of dementia [1]. In contradiction, a single study indicates that the incidence of postoperative cognitive deficit (POCD) decreases if hypnotic depth is deep [2]. Unfortunately the study did not sum up the amount of anesthetic drug load, since this would have clarified if the amount of anesthetics used is associated to POCD and dementia. Another possibility is that stress and noxious stimulation induced by light anesthesia results in POCD, whereas deep anesthesia protects from it or inhibits implicit memory.

The investigators' prospective randomized trial is underway to verify the impact of anesthetics and narcotic depth upon grade of dementia and incidence of early postoperative cognitive dysfunction on postoperative day 1 as well as the incidence of delirium within a 90 day period.

The investigators' hypothesis is that the incidence of POCD and delirium and the degree of early cognitive dysfunction is less when anesthetic and vasoactive drug load is less in the BIS- guided anesthesia group with the superficial but sufficient anesthesia level.

Inclusion Criteria:

• adults older than 70 years
• major surgery ( spine, orthopedic, urologic, gynecology, abdominal)

Exclusion Criteria:

• adults younger than 71 years
• major blood loss surgery
• allergy to soja oil, nuts, other ingredients of propofol
• patient wants to have spinal or regional anesthesia only